SiC Oxidation Protective Coating for Graphite Mould

Abstract

In order to exploit the anti-oxidation property of graphite mould, a new type of oxidation protective coating is produced by a pack cementation diffusion coating technique. To enable this material to be used at high temperatures, graphite moulds are coated with Si/SiC slips. The anionic dispersant is added to disperse the slip uniformly, of which the optimal amount is evaluated with viscosity. The graphite mold specimens are surface-modified at 100 °C for 10 minutes in a non-polar polymer aqua-solution, considering the uniform wettability of slip. The surface-modified graphite mold specimen shows better wettability than the nonsurface- modified graphite one when coating process is performed through the slip. The interface-reaction of the specimens is performed at 1450 °C in a reduction atmosphere. The microstructure and composition before and after the pack cementation are observed by SEM and EDS, and the phase identify was performed with XRD. The layer of specimens double-coated by the pack cementation and Si/SiC slip coating method is stable, and properties of SiC coating layer formed on the graphite mould surface are dependent on particle size of starting material, Si, and open-pore size of the graphite mould surface. It is found that larger particle size of Si and smaller open-pore size of the graphite mold were the preferable conditions for the interface produces an optimal reaction which anti-oxidation coating.